Techniques for driving an elastic endless belt by engaging a sprocket with a plurality of engaging portions (core bars) on the endless belt are known. One such technique prevents tooth jumping, which is caused by the driving force or by foreign material getting stuck, by providing the outer surface of the core bars on the sprocket side with a semicircular cross-sectional shape and engaging and catching only a slight portion of the area near the tooth root of the sprocket (for example, see PTL 1: JP 2011-152851 A (PTL 1)).